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Re: st: Zero Inflated Models

From   Ronan Conroy <[email protected]>
To   "statalist" <[email protected]>
Subject   Re: st: Zero Inflated Models
Date   Mon, 6 Oct 2003 11:43:05 +0100

on 06/10/2003 11:21 am, atobias at [email protected] wrote:

> Dear statalisters,
> Does anybody know if there is any ado available to fit Zero Inflated
> Normal models, that is like ZIP but for normally distributed data. For
> information, this models could be useful to fit environmental data,
> such as pollen or rainfall levels.

Interesting problem.

With rainfall, I guess it either rains or it does not, so there may be a two
step model involved. How about -heckman-?

With pollen, on the other hand, the failure to observe any pollen at all
means that pollen levels are below detection. If you are willing to assume
that the normal distribution of the observed levels (are they normal?)
continues below the threshold of detection, then �intreg- may be the way to

Ronan M Conroy ([email protected])
Lecturer in Biostatistics
Royal College of Surgeons
Dublin 2, Ireland
+353 1 402 2431 (fax 2764)

Bombing our way to a perfect world...

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